1. Field of the Invention
The present invention relates to an attachment plug which is provided with an earth terminal pin.
2. Description of the Background Art
FIG. 12 is a perspective view showing a conventional attachment plug which is provided with an earth terminal pin. Referring to FIG. 12, a pair of power terminal blades 23 and 24 and an earth terminal pin 25 are mounted on the front surface of a holder 22 for an attachment plug 21. The attachment plug 21 provided with the earth terminal pin 25 is inserted in a grounded power plug socket, which is provided with a pair of slots corresponding to the power terminal blades 23 and 24 as well as a hole of an earth electrode for receiving the earth terminal pin 25. Such a plug socket is mainly used in a factory, on the site of construction, or the like.
In the conventional attachment plug provided with an earth terminal pin as shown in FIG. 12, no problem is caused when the same is inserted only in such a grounded plug socket. However, this attachment plug cannot be inserted in a plug socket which has no hole of an earth electrode for receiving the earth terminal pin 25. A general plug socket for domestic use etc. has no such hole of an earth electrode. Therefore, a problem is caused in relation to an attachment plug for an electric appliance such as a cord reel, which is applicable to domestic use in addition to use in a factory, on the site of construction, or the like.
FIG. 12 shows an adapter 31 which is generally employed to enable insertion of such an attachment plug in the aforementioned two types of power plug sockets. Power terminal blades 33 and 34 are provided on the front surface of a holder 32 for the adapter 31. The holder 32 is further provided on its rear surface with a pair of holes (not shown) for receiving the power terminal blades 23 and 24 of the attachment plug 21, as well as a hole (not shown) for receiving the earth terminal pin 25. The power terminal blades 23 and 24 of the earth terminal pin 25 are inserted in the holes which are provided on the rear surface of the adapter 31, so that the power terminal blades 23 and 24 are electrically connected with the power terminal blades 33 and 34 of the holder 31 while the earth terminal pin 25 is electrically connected with an earth terminal cord 35. Thus, the attachment plug can be inserted in a power plug socket having no earth electrode through the power terminal blades 33 and 34, which are provided on the front surface of the adapter 31. Further, the attachment plug can be grounded through the earth terminal cord 35, if necessary.
However, such an adapter 31 may be lost during use, since the same is not integrated with the attachment plug. Although the adapter 31 may be connected to the attachment plug with a cord or the like so that the former is not separated from the latter, the attachment plug is hard to handle in this case. Even if the adapter is connected to the attachment plug with a strong cord, the same may still be lost during use.
Further, the product cost is increased due to the adapter, which is not integrated with the attachment plug.